Most thrips in greenhouse are females. Adult females may live for approximately 30 to 45 days and lay from 2-10 eggs per day which are inserted into plant tissue. The first two larval stages remain protected in the tender young growth. After the 2nd instar larvae stops feeding, it migrates to the base of the plants and enters the growing medium to pupate. Adults emerge in two to five days, depending upon temperature. Thrips development occurs between 50˚F and 90˚F. They can survive cooler temperatures than 50˚F; however, there is no development at that temperature.
The bacterium Agrobacterium tumefaciens is a soil borne pathogen that causes crown gall on many types of plants. In greenhouse crops, Crown Gall has been diagnosed in recent years on mums, argyranthemum and osteospermum and this year it has been found in some of Selecta's lobelia production. Selecta found symptomatic plants in four varieties of Magadi Lobelia: Blue, Compact Dark Blue, White and Basket White. Selecta sent information out to their customers and is discontinuing shipments of Lobelia for this spring.
Treatments for fungus gnats are best directed against the larval stage. Many growers use beneficial nematodes Steinernema feltiae sold under the trade names of Nemashield, Nemasys, Entonem or Scanmask applied as a drench. Fungus gnat larvae are killed in one or two days by the symbiotic bacterium that dissolves their internal contents.
It has been an interesting winter. Given the warm temperatures this year, growers are advised to open up overwintering greenhouses on warm days to ventilate. Either roll up sides, open doors, use fans, depending on the type of overwintering greenhouse. Ventilating will lower the relative humidity. Greenhouses that are closed up will result in moisture buildup and encourage plant diseases to develop. Also, take time to inspect plants in overwintering houses, particularly for disease and injury caused by rodents.
Small greenhouses (< 4,000 sq.) can be scouted as one unit. Larger greenhouses should be divided into 2,000 to 3,000 sq. ft. sections for ease of scouting. Scout propagation areas at least every 3 to 4 days. Use your prior experience to determine how many plants and which plants to inspect (those that are most susceptible to pests or diseases in your greenhouse). The more plants or locations inspected, the more likely it is that a problem will be detected in a timely manner, when treatments are the easiest.